264 BULLETIN OF THE 



this not only in OphiogJi/pha (5), but in most other genera, bears one or more 

 tentacle-scales, under the form of outer mouth-papillae ; while what may exactly 

 be called mouth-papillae (d) are apt to stand on the mouth-frames. This distinc- 

 tion, however, is only one of convenience as applied to parts really homologous. 

 Thus in Ophioglypha the two rows of scales belonging to the second pair of 

 mouth-tentacles stand respectively on a plate which is really an overgrown outer 

 mouth-papilla (see under Pectinura marmorata), and on the side mouth-shield 

 (partly, also, on the mouth-frames ?). The first pair of mouth-tentacles, in the 

 same genus, are duly furnished with their own scales, which stand, as usual, on a 

 ridge of the jaw. All the complex arrangement just described may be most 

 clearly seen in 0. Lymani. 



The integument which encloses the disk is, properly speaking, covered, or beset, 

 with calcareous plates, which, in the young, are six in number, to wit, the largest 

 in the centre and the other live in a close circle round it, one opposite the base of 

 each arm. In some genera the secretion of lime is stopped in the disk integument 

 at an early period ; and, in the adult, nothing is to be found but a few minute 

 grains buried in the skin, while the general surface of the disk is smooth and 

 fleshy. Such genera are said to be naked (Ophiomyxa, Ophiarthrum, Figs. 1, 2, 

 C). Others are equally called naked where a thick skin covers a regular scaly 

 coat (Ophiopsila). In many genera the disk is plainly covered with plates, which 

 may be finely imbricated scales (Amphiura, Fig. 2, F) or coarser and thicker 

 ones irregularly arranged (Ophioglypha, Figs. 1, 2, E), or thick angular pieces 

 set side by side on the same level, like a mosaic (Ophiolcpis, Ophiomusium). Then 

 there are genera in which the scale coat is beset, or even hidden, by appendages. 

 These may be spines (Ophiothrix, Figs. 1, 2, D) ; or scattered grains (Ophiocoma , 

 Fig. 1, B) ; or grains so closely set as to completely hide the disk, radial shields 

 and all, except the mouth-shields (some species of OpJiiura, Fi^s. 1, 2, A). There 

 is one genus (Ophiopsa7nmium) in which the disk and upper surface of the arms 

 are covered, first by a smooth integument, and this again by a close granulation. 

 The radial shields are to be seen in all species in which the scale coat is visible, 

 and the mouth-shields are never hidden except in a few species which have a very 

 thick, naked integument. 



PLATE II. 



Spines and Stumps of the Disk of Ophiothkix. 



All the figures are enlarged about thirty diameters. 

 Figs. 1-14 Oph loth rix cch inata. 



" 15-29 " lusitanica. 



" 30-36 " pentaphyllum. 



" 37-44 " fragilis. 



" 45-55 " quinqucmaculata. 



1, 2, 3, a spine and two stumps, 0. echinata, original of Mull, k Trosch. 4-9, 



